1. Field of the Invention
The present invention relates to an image display apparatus, and an image signal processing method, which carry out processing of an image signal supplied to a plurality of display devices having different optical characteristics, using a common display driving circuit, and a program for implementing the method, and a storage medium storing the program.
2. Description of the Related Art
Conventionally, there has been known a liquid crystal display apparatus which, when carrying out brightness adjustment of an image signal, can realize sufficient gradation displays, even if the amplitude of the image signal is reduced. Further, there has been known a camera integrated-type VTR provided with a direct view-type liquid crystal display panel and a finder view-type liquid crystal display panel. With this camera integrated-type VTR, a method is employed in which the two display panels are each driven by a dedicated driving circuit. This is due to the fact that optical characteristics such as gamma, brightness, contrast, and white balance, differ according to the type of liquid crystal display panel, and thus, an independent driving system must be provided for each type.
FIG. 5 is a block diagram schematically showing the electrical configuration of a conventional liquid crystal display apparatus. This liquid crystal display apparatus is comprised of a direct view-type liquid crystal display panel 110, a first liquid crystal driving circuit 102a that drives the direct view-type liquid crystal display panel 110, a finder view-type liquid crystal display panel 111, and a second liquid crystal driving circuit 102b that drives the finder view-type liquid crystal display panel 111.
The first liquid crystal driving circuit 102a includes a contrast adjusting circuit 103a that adjusts the amplitude of an image signal, a brightness adjusting circuit 104a that adjusts setup levels of the image signal, a gamma adjusting circuit 105a that adjusts gamma characteristics of the image signal, and a memory 106a. The second liquid crystal driving circuit 102b includes a contrast adjusting circuit 103b that adjusts the amplitude of the image signal, a brightness adjusting circuit 104b that adjusts setup levels of the image signal, a gamma adjusting circuit 105b that adjusts gamma characteristics of the image signal, and a memory 106b. 
With the image display apparatus having the above configuration, when an image signal that has been converted to the RGB format by a decoder, not shown, is inputted via an input terminal 101, the image signal is supplied to the first liquid crystal driving circuit 102a, where signal processing is carried out on the image signal by the contrast adjusting circuit 103a, the brightness adjusting circuit 104a, the gamma adjusting circuit 105a, an inversion circuit, not shown, etc., and then the processed image signal is supplied to the direct view-type liquid crystal display panel 110, whereby an image is displayed. At this time, adjustment values for carrying out the above signal processing are set to the contrast adjusting circuit 103a, the brightness adjusting circuit 104a, and the gamma adjusting circuit 105a, based on first control data 107 that is stored in the memory 106a. 
Further, the image signal that is inputted via the input terminal 101 is simultaneously supplied to the second liquid crystal driving circuit 102b. After signal processing is carried out on the image signal by the contrast adjusting circuit 103b, the brightness adjusting circuit 104b, the gamma adjusting circuit 105b, an inversion circuit, not shown, etc., the image signal is supplied to the finder-type liquid crystal display panel 111, whereby an image is displayed. At this time, adjustment values for carrying out the above signal processing are set to the contrast adjusting circuit 103b, the brightness adjusting circuit 104b, and the gamma adjusting circuit 105b, based on second control data 108 that is stored in the memory 106b. 
In this way, with the conventional image display apparatus, it is possible to set optimum settings for the direct view-type liquid crystal display panel and for the finder-type liquid crystal display panel.
However, with the above conventional image display apparatus, further improvements are demanded in the following points. That is, the provision of two sets of liquid crystal driving circuits on the image display apparatus is disadvantageous in terms of the area for mounting component parts, power consumption, and cost, and thus, it is difficult to provide an apparatus having a small size, reduced power consumption, and a low cost.
Further, when a plurality of liquid crystal panels such as a direct view-type liquid crystal display panel, and a finder view-type liquid crystal display panel, are employed in a camera integrated-type VTR, since the optical characteristics of the liquid crystal panels differ, the optimum set values of brightness, contrast, gamma, and the like, differ between the liquid crystal panels. In addition, in recent years, white light emitting diodes (hereinafter referred to as “white LEDs”) are used as a light source for backlight for liquid crystal displays. However, the white LEDs have large variations in chromaticity due to their characteristics. Conventionally, such variations are corrected on the liquid crystal panels by providing offset for the setup of R, G, B image signals. Therefore, even if the optical characteristics of the direct view-type liquid crystal display panel and the finder view-type liquid crystal display panel were the same, if the chromaticity of the backlight that is combined differs, the optimum set values for image signals become different between the liquid crystal panels.
As mentioned above, if these two liquid crystal display panels are driven by respective dedicated driving circuits, it is possible to supply an optimum image signal for each liquid crystal display panel. However, in this case, two sets of liquid crystal driving circuits are used, which is disadvantageous in terms of the area for mounting component parts, power consumption, and cost, and thus, it is difficult to provide an apparatus having a small size, reduced power consumption, and a low cost.
On the other hand, if the two liquid crystal panels are driven by a single driving circuit, optimum image signals cannot be supplied to both of the liquid crystal display panels, and there arises a problem that the image quality of either one of the display panels becomes degraded.